The present invention relates to an advancing cylinder for use in a printing machine, particularly in a high-speed offset printing machine, which has associated therewith an arrangement for transferring a respective sheet to be advanced through and printed upon in the printing machine, from a predetermined location on a support of the advancing cylinder, to a predetermined position on the periphery of the advancing cylinder.
It is well known that in printing machines, such as offset printing machines, in which images are to be printed on a series of sheets which are consecutively advanced through the printing machine, it is necessary to so transfer each respective sheet at least from the feeding table to the first advancing cylinder of the printing machine that the respective sheet assumes a predetermined position on the periphery of this advancing cylinder so that respective image or images is subsequently printed exactly on the desired zone of the respective sheet for each sheet of the series. Some conventional printing machines resort to the use of so-called stop drums or of rocking grippers which engage the respective sheet, which has been previously aligned and stopped on the feeding table or the like, and accelerate the respective sheet to the peripheral speed of the advancing cylinder to transfer the respective sheet to other grippers which are mounted in the advancing cylinder only when the respective sheet has achieved the above-mentioned peripheral speed of the advancing cylinder. In these conventional machines, a direct transfer of the respective sheet from its aligned and stopped position to the grippers of the advancing cylinders which orbit with and at the speed of rotation of the advancing cylinder, is no longer possible at high speeds of rotation of the advancing cylinder, especially in view of the fact that the accuracy of the positioning of the respective sheet on the advancing cylinder, which is especially, but not exclusively, required in multicolor printing, cannot be achieved under these circumstances. Thus, the utilization of the above-mentioned intermittently operating stop drums or rocking grippers was heretofore the precondition for achieving both high printing speeds and accurate positioning. However, these arrangements assume a substantial amount of space at the peripheral region of the advancing cylinder and simultaneously obstruct the view of the upstream end of the printing machine.
In order to avoid these difficulties, it has already been proposed in the German published patent application No. 1,954,559 to use only a single gripper system arranged in the interior of the advancing cylinder, particularly in a recess or depression thereof, the gripper system being mounted for rocking or pivoting relative to the advancing cylinder about the axis of rotation thereof. This internal gripper system is supposed to unite the functions of the heretofore customary external rocking grippers as well as of the cylinder grippers. This space-saving arrangement renders it possible not only to arrange an additional printing device at the periphery of the same advancing cylinder, but also to increase the printing speed as compared to what was possible before, particularly in view of the fact that, as a result of this particular construction, a separate rocking gripper system having a substantial rocking range and also comparatively high mass or inertia can be eliminated, and with it also an additional transfer of the respective sheet of the series.
It is also known from the German published patent application No. 1,118,811 to so construct a sheet-transfer system for a cylinder as to include grippers which are mounted on rocking arms which, in turn, are mounted on a pivot shaft which is arranged eccentrically to the axis of rotation of the cylinder. In this arrangement, the grippers emerge beyond the periphery of the cylinder during the movement of the rocking arms in their range of pivoting; however, the grippers of this conventional arrangement are actuated as to their movement by means of control pins which are stationarily arranged on the frame of the printing machine or a similar support and which engage suddenly. The movements which are produced in this manner are limited to the smallest angle of rotation of the cylinder so that high accelerations and relatively high instantaneous speeds are obtained.